Synthesis of ketones by isomerisations
An operationally simple palladium-catalyzed isomerization of highly substituted allylic alcohols and alkenyl alcohols is applicable to a broad range of substrates and displays a wide functional group tolerance. Carbonyl compounds can usually be isolated in high chemical yield. Experimental and computational mechanistic investigations provide evidence for a chain-walking process consisting of repeated migratory insertion/β-H elimination sequences.
E. Larionov, L. Lin, L. Guénée, C. Mazet, J. Am. Chem. Soc., 2014, 136, 16882-16894.
Phenanthroline and tert-butoxide are powerful radical initiators, that enable a catalyzed transition-metal-free allylic isomerization of allylic alcoholsvia a base-promoted allylic anion pathway. The radical pathway is supported by experimental evidence that includes kinetic study, kinetic isotope effect, isotope-labeling experiments, trapping experiments, and EPR experiments.
H.-X. Zheng, Z.-F. Xiao, C.-Z. Yao, Q.-Q. Li, X.-S. Ning, Y.-B. Kang, Y. Tang, Org. Lett., 2015, 17, 6102-6105.
Grubbs' 2nd generation and Hoveyda-Grubbs' ruthenium alkylidenes are shown to be effective catalysts for cross-metatheses of allylic alcohols with cyclic and acyclic olefins, as well as isomerization of the resulting allylic alcohols to alkyl ketones in a single-flask process that provides highly functionalized, ketone-containing products.
D. Finnegan, B. A. Seigal, M. L. Snapper, Org. Lett., 2006, 8, 2603-2606.
An alternative pathway to the Wacker oxidation of internal olefins involving epoxidation of trans-alkenes followed by a mild and highly regioselective isomerization gives ketone isomers in good yield.
J. R. Lamb, M. Mulzer, A. M. LaPointe, G. W. Coates, J. Am. Chem. Soc., 2015, 137, 15049-15054.
DABCO-mediated Meinwald rearrangements of 2-aryl-, alkenyl-, and alkynylepoxides provide the corresponding methyl ketones chemospecifically in good yields. The reaction offers readily accessible starting materials, a wide substrate scope, a transition-metal- and acid-free environment, and chemospecificity in the isomerization of epoxides.
S. Li, Y. Shi, P. Li, J. Xu, J. Org. Chem., 2019, 84, 4443-4450.